Latest Situation Updates

Stem rust attacks in Sweden heralds the return of a previously vanquished foe

Stem rust. Almunge, Sweden 2017. (Credit: Anna Berlin, SLU)

Scientists at the Swedish University of Agricultural Sciences (SLU) are reporting that stem rust has returned to Sweden. In a recently released press release, lead researcher Anna Berlin from the Department of Forest Mycology and Plant Pathology outlines an unusually intense stem rust attack in wheat fields in Almunge, Uppland in the summer of 2017. The last major stem rust outbreak reported from Sweden was in 1951, so this latest outbreak and the initial indications that it is a sexual population emerging from barberry is a major cause for concern.

Full details of the report from the Swedish University of Agricultural Sciences (SLU) can be found at:

https://www.slu.se/en/ew-news/2017/11/stem-rust-attacks-in-sweden-heralds-the-return-of-a-previously-vanquished-foe/

Detection of stem rust race RRTTF in Ecuador. A potentially important new race for the Americas

A team of scientists from Ecuador, Canada and the USA recently published on the detection of race RRTTF based on samples collected in Ecuador in February 2016. The study led by Dr Charlie Barnes from the Instituto Nacional de Investigaciones Agropecuarias (INIA), Quito, Ecuador has just been published in Plant Disease. Race RRTTF is distinctive by its combined virulence to genes Sr38 and Sr13 and poses a significant threat to wheat production in North and South America as a large proportion of current commercial cultivars are known to be susceptible. The origin of Pgt race RRTTF in Ecuador is unknown, but it is similar to previous isolates of RRTTF from Asia (Pakistan), eastern Africa (Ethiopia), and the Middle East (Yemen). It is unknown whether race RRTTF is a recent long-distance exotic introduction into Ecuador, or a de novo variant of an existing South America lineage that was introduced earlier. Further study is needed to determine how widespread this race is in Ecuador and its potential to migrate to large-scale wheat production areas in South and North America.

Study identifies likely scenarios for global spread of devastating crop disease

New research reveals for the first time the most likely months and routes for the spread of new strains of airborne ‘wheat stem rust’ that may endanger global food security by ravaging wheat production across Africa, the Middle East, Asia and the wider world.

Stem rust (or black rust), named for the blackening pustules that infect plant stems, caused devastating crop epidemics and for centuries before being tamed largely by use of resistance genes.

Since the turn of the century, however, aggressive new strains have emerged – such as ‘Ug99’, first detected in Uganda in 1999 – that infect widely grown varieties of wheat. These diseases threaten to disperse trillions of pathogenic fungal spores on winds across countries and continents.

The fear is that these airborne and highly virulent strains could spread from known sites to some of the world’s most important ‘breadbasket’ regions, such as the Punjab in South Asia, where these strains have not yet been detected.

Now, a team of scientists of the University of Cambridge, the UK Met Office and CIMMYT (International Maize and Wheat Improvement Centre) have adapted modelling systems previously used to forecast, ash dispersal from erupting volcanoes and radiation from nuclear accidents (NAME), to predict when and how Ug99 and other such strains are most likely to spread.

The research, published today in the journal Nature Plants, quantifies for the first time the circumstances – routes, timings and outbreak sizes – under which dangerous strains of stem rust pose a threat from long-distance dispersal out of East Africa to the large wheat-producing areas in India and Pakistan.

The results highlight the role of Yemen as a potential ‘stepping stone’ for the transmission of the disease between continents.  The key scenario for disease spread is from Yemen directly to Pakistan or India.  In case of a large outbreak in Eastern Yemen results indicate a 30% chance for transmission to occur.

Another important scenario for wheat rust to spread is from Yemen through Middle Eastern countries, in particular Iran, to Central and South Asia. If Iran were to suffer a moderate outbreak of Ug99 – on more than 1000 hectares – then spores would likely spread to Afghanistan, and from there potentially further to the northern plains of Pakistan and India. However, transmission along this route is restricted to a relatively short time-window in March and April, before wheat is typically harvested in South Asia.

“New races of wheat rust are threatening wheat worldwide, and we need to know which areas are at risk,” said senior author Prof Chris Gilligan, from Cambridge’s Department of Plant Sciences.

 “From our work, we now believe that if we start to see Ug99 or other new wheat rust strains take hold in Yemen in early Spring then action must be taken immediately to mitigate the risk of further spread.”

 

Network map of the atmospheric transmission of spores causing wheat stem rust.

(A) Long-distance dispersal network of spores between all major wheat producing countries in Southern/East Africa, the Middle East and Central/South Asia. Nodes represent countries; communities of the same colour indicate regions with high airborne connectivity; the size of nodes indicates node-strength; pie charts show the fraction of out-strength to total node strength (indicating donor and receptor countries).

(B) Spore transmission frequencies along principal migration routes in the Rift Valley zone for the scenario of large outbreaks.

However, the modelling work also offers some encouraging news: the airborne transmission of the disease from East African countries directly to South Asia is highly unlikely, with transmission events possible only on less than one day a year.

The scientific team used field disease surveys from the International Maize and Wheat Improvement Centre (CIMMYT) and weather data from the UK Met Office as key input for the modelling framework.

This research has allowed us to obtain the first quantitative estimates of long-term airborne spore transmission frequencies for different outbreak scenarios. We compiled risk assessments for pathogen dispersal from key disease locations to important wheat-producing countries. These assessments can effectively inform surveillance and control strategies,” said Cambridge’s Marcel Meyer, the study’s first author.

The team say their work, including 3-D spore dispersal animations and a catalogue of spore dispersal trends (indicating likely directions, frequencies, pathogen loads), provides new ways to raise awareness, communicate risks, and inform agricultural stakeholders.

Their modelling framework can be applied as a tool to analyse risks in case new disease strains should be uncovered in other geographic areas. This has already recently helped in estimating dispersal risks from detection sites of related wheat rust diseases in Europe and Siberia. In ongoing work the team is developing an Early Warning System forecasting disease risk in Ethiopia, East Africa’s largest wheat producing country.

The combined expertise from plant sciences and atmospheric dispersion sciences has delivered ground breaking tools that highlight the risks, and support the management of the devastating potential of these diseases,” said Dr Matthew Hort, co-author from the UK’s Met Office.

Source: University of Cambridge

Author contacts:

Chris Gilligan, University of Cambridge: +44 7964 598 147; cag1@cam.ac.uk

Marcel Meyer, University of Cambridge: mm2086@cam.ac.uk

Matthew Hort, UK Met Office: +44 (0)1392 886242; matthew.hort@metoffice.gov.uk

Dave Hodson, CIMMYT-Ethiopia: d.hodson@cgiar.org